1. Field of the Invention
This invention relates to a permanent magnet powder material and, more particularly, to a permanent magnet powder material which has superior magnetic properties such a high coercive force and which can be formed into bonded magnets by being blended with synthetic resin, nonmagnetic metal, etc., or bulk compacted magnets having a full density by consolidation of the powder at high temperatures.
2. Description of the Prior Art
In conventional alloys composed of rare earth elements(R), transition metals(T) and semimetal elements(M), high coercive force permanent magnet powders, the crystal grain size, which is the crystal grain size resulting from recrystallization of an amorphous state, have been disclosed in Japanese Patent Publication No. 1-28489.
In this Japanese Patent Publication, an alloy having a specific composition is amorphized by rapidly cooling from a liquid state or by sputtering ions of the alloy onto a substrate and rapidly cooling the ions. The resultant amorphous alloy material is recrystallized by a heat treatment at an appropriate temperature. In such manner, stable permanent magnet powders having a high coercive force can be obtained.
The magnetic properties of permanent magnet powders made by rapidly cooling an alloy melt may greatly vary depending on the composition and cooling conditions. Among the magnetic properties, the maximum energy product (BH)max is the most important parameter and, in order to increase this parameter, it is necessary to increase the residual magnetic flux density (Br), coercive force (iHc) and squareness of the demagnetization curve.
However, generally, conditions providing a large residual magnetic flux density result in a reduced coercive force. On the other hand, when conditions providing a large coercive force are applied, a lowered residual magnetic flux density results. Therefore, values of maximum energy product are limited to certain levels, taking into consideration these two parameters. In order to obtain a higher level of maximum energy product, it is essential to improve the squareness in a demagnetization curve. Therefore, the proper choice of alloying elements and compositions are very important.
Hk/iHc is used as a parameter for the squareness of a demagnetization curve wherein Hk is the value of H at 4.pi.I=0.9Br in a demagnetization curve represented by 4.pi.I-H . This relationship is shown in FIG. 3.